The miniaturization of electronic devices such as integrated circuits continues to drive the costs of electronic products down even as the performance of these products increases. The development of improved lithographic methods and other fabrication processes as well as improved packaging and circuit interconnection methods have been important factors this trend.
While improvements in fabrication processes for miniaturization permit inexpensive manufacture of ever smaller devices, the interconnection of smaller devices can be difficult and expensive. In addition, the operation of smaller devices presents additional difficulties. Such smaller devices frequently are required to perform at least the same functions as the larger devices that they replace, and in many cases are expected to perform these functions faster and at a lower cost. A small device that operates at high speeds tends to generate large amounts of heat in a smaller volume, and dissipation of this heat is essential to avoid damage to the device so that the device has an acceptable time to failure. Therefore, improved circuit packages and packaging methods are needed that permit improved heat transfer.
Another significant problem in the use of integrated circuits is packaging the integrated circuit in such a way as to electrically connect to many, densely spaced input/output electrical connections. If the input/output electrical connections must be spread out to permit electrical connections to other integrated circuits, other circuits or circuit components such as printed circuit boards, then much of the advantage of integrated circuit miniaturization is lost.
One method of packaging integrated circuits for electrical connection to a printed circuit board is the so-called ball grid array (BGA) package. A BGA package includes a semiconductor die (an integrated circuit) that is attached to a substrate. Electrical connections are made from the die to the substrate with bond wires that are attached to bond pads provided on the die and the substrate. The bond pads on the substrate are electrically connected to an array of solder balls or bumps, and these solder balls are used to bond and make electrical connection to the printed circuit board. BGA packages are described in, for example, Tsuji et al., U.S. Pat. No. 5,930,603, Tsunoda et al., U.S. Pat. No. 5,914,531, and Tsuji et al., U.S. Pat. No. 5,293,072.
Not only are BGA packages more compact than other packages, BGA packaged devices generally have superior thermal and electrical properties. The solder balls provide an excellent thermal path for the removal of heat from the semiconductor die as well as providing low resistance, low inductance electrical connections. Nevertheless, improved BGA packages that provide even denser interconnections and greater heat removal are needed.